Waterlaid felt



Patented Mar. 10, 1936' PATENT OFFICE WATEBLAID FELT I Milton 0. Sohurand Walter L. Hearn, Berlin,

N. 11., assignors to Brown Company, Berlin, N. H., a corporation ofMaine No Drawing. Application November 19, 1932,

Serial No. 643,544

2 Claims.

This invention relates to porous and absorptive waterlaid felts such asare designed to undergo impregnation with binders of various kinds.

We have found that in making waterlaid felts, it is highly advantageousto blend 2. refined, preliberated pulp, preferably refined wood pulp,and rag pulp. Such a blend is advantageous, not only by reason of thefact that the rag pulp may be prepared directly from waste rags, whichare far less expensive than refined wood pulp, but also by reason of thefact that the felts made from such a blend are, as will hereinafterappear in greater detail, of improved characteristics. In makingimpregnated products, e. g., bituminized sheets or ielts, from such ablend, it is distinctly preferable that the refined wood pulp bemaintained in substantially unhydrated condition, whereas the rags maybe reduced to a beaten or hydrated halfstufi by beating as ordinarily ina hollander or heater engine. The blend made up of substantiallyunhydrated but refined wood pulp and hydrated but unrefined rag pulp,may be formed into a waterlaid felt. The felt may be impregnated withvarious binders, e. g., latex, natural or synthetic resins, celluloseester solutions, waxes, bitumens, or other binders of a thermoplastic,water-dispersed, or dissolved Va riety. For instance, the felt may bebituminized to form a product possessed of improved utility in theroofing and flooring industries.

While not limited thereto, we shall hereinafter deal with our inventionas applied to the manufacture of bitumlnized sheets of a characterhighly prized in. the roofing and flooring in dustries. In theseindustries, waste rags have heretofore been employed as the raw materialfor making the felt base, which is bituminized and put through thefinishing operations. In the roofing industry, the bituminized sheet issurfaced with talc, sand, mica, or the like, when roll roofing is inview, or is coated with blown asphalt and then surfaced with crushedslate or similar granular material when roofing shingles are in view. Inthe flooring industry, the bituminized sheet is put through a printingor painting machine, which applies an ornamental coating to the sheet.In both these industries, the finished article has heretofore beeneasy-tearing and of poor pliancy or flexibility.

It has been found that when the felt base is made from refined woodpulp, and more especially refined wood pulp in a substantiallyunhydrated condition, the bituminized felt is vastly improved in itstear resistance and in other respects. We have discovered that,notwithstanding the inferiority of a rag base felt, it is possible torealize a felt which represents an improvement over the refined woodpulp base felt by using both rag pulp and refined wood pulp as thefelt-making fibrous materials. In other words, we have found that ablend or mixture of the two fibrous materials gives better results thandoes either fibrous material alone. This holds true especially when therefined wood pulp is used in amount preponderating over the rag pulp andis kept from becoming substantially hydrated before the felt-makingoperation, whereas, on the other hand, the rag pulp is hydrated to theextent which necessarily ensues from its having been produced by thebeating and reduction of rags in water in the ordinary hollander orbeater engine.

A specific example of procedure falling within the purview of ourinvention and applicable in the manufacture of roofing and flooringmaterials may be practised substantially as follows. The usual ragscurrently employed in making roofing and flooring felts may be used inamount up to about 50% by weight of the fibrous furnish prepared in thebeater engine. Therags may contain some wool fiber in addition to thecotton. The usual hollander may be charged with the rags and suflicicntwater to ensure circulation, whereupon beating of the rags may becarried on until the fibers have been reduced to the desired extent andan aqueous pulp suspension or rag halfstuff fit for felt-making has beenproduced. The beater roll may then be raised from the bedplate and therefined wood pulp may then be added to the rag halfstufi and the enginekept running until a physically homogeneous mixture of the two kinds offiber has been effected. The refined wood pulp is hence kept in asubstantially unhydrated state by reason of the fact that the beaterroll is operated merely to effect a mixing of such pulp with thepreviously beaten rags, and further by reason of the fact that refinedwood pulp is comparatively difficultly hydratable. The mixed fiberfurnish is delivered from the beater engine into the stock chest,wherein it is diluted to the appropriate consistency for delivery to thefelt-making machine. The diluted pulp is further thinned with largevolumes of water, most of which is white water recirculated from theforming or wet end of the felt machine. It is highly advantageous thatthe pulp be fed onto the felt-forming screen or wire cloth in a highlydiluted state, in order that good formation shall be obtained. In thecase of a cylinder mould, for

example, it is preferred to operate at consistencies 55 lid below, say,about 0.35%, in order to avoid lumpy definite range, depending uponwhether the felt is to be bituminized for roofing or for flooringpurposes.

In connection with roofing, where it is desired that the felt absorb amaximum amount of asphalt, the compactness may be comparatively low,somuch so that the felt will be able to absorb up to about 250% to 300% ormore of its own dry weight of asphalt. In such case, we may preparefelts having a compactness ranging from about to about 45. When feltsfor fiooring purposes are in view, the compactness should be higher, inorder that the bituminized felts may have the desired mechanicalproperties, especially resistance to indentation or distortion, withoutbeing so dense that difiiculties will be encountered, especially duringimpregnation. For fiooring purposes, therefore, our felts' arepreferably prepared so as to have a compactness ranging from about 50 to70. By compactness, we mean the ratio of the basis weight of the felt interms of pounds per 2880 square feet, divided by the felt thicknessexpressed in hundreds of an inch.

The felts prepared as hereinbefore described may be put through abituminizing operation, such as is currently practised in the roofingandfiooring industries. The bituminized roofing felt may, as alreadyindicated, contain up to about 250% to 300%, or more, of its own dryweight of asphalt, whereas the bituminized flooring felt may containmuch less asphalt, say only about 100% to 175%, more or less, of its owndry weight of asphalt. The bituminized roofing felt may then be finishedin the usual manner, depending upon whether roll roofing or roofingshingles are in view. So, too, the bituminized flooring felt may beornamentally finished in accordance with the conventional finishingsteps employed in fiooring manufacture.

There. are various important advantages in using rag pulp along withrefined, preliberated, substantially unhydrated cellulose pulp in thefiber furnish employed for making felts to be bituminized ashereinbefore described. Aside from the fact that unrefined ragsconstitute an inexpensive raw material, being far less expensive thanalkali-refined, chemically preliberated wood pulp, the rag halfstuifprepared in the beater engine enhances the qualities of the raw or unimpregnated felt without detracting from the qualities of thebituminized felt. The felt of the present invention in its raw orunimpregnated state is superior to a felt made substantially entirelyfrom refined and substantially unhydrated wood pulp. Thus, in suchimportant respects as tensile strength, tear resistance, andflexibility, the raw or unimpregnated felt of the present inventionconstitutes a definitely superior article. In connection with thequality of improved flexibility, it might be mentioned that during thesaturating and finishing operations, the felt generally undergoesflexing about a great many rollers of comparatively small diameter, sayabout 4 inches. When a felt is made practically wholly from refined butsubstantially unhydrated wood pulp, the fiexing which it undergoes, ashereinbefore described, is apt to cause rupture of the felt surface,owing to the tendency of the surface fibers to separate or part from oneanother under flexing and/or tension. This tendency exists to a muchreduced degree in the felts of the present invention. The improvementeffected through the inclusion of pulped rags in the felt-making furnishis surprising, particularly when one considers the fact that rag pulpalone yields a felt of a stiff and boardy character, which not onlytends to crack or break comparatively easily when bent upon itself, butwhich after bituminization has relatively low pliancy and tearresistance.

While the felts of the present invention may be made from variousproportions of rag pulp and refined but substantially unhydrated woodpulp, nevertheless, as already indicated, we prefer to employ apreponderating proportion of the refined but substantially unhydratedwood pulp. Indeed, we prefer to prepare a fiber furnish containing notmore than about 35% to 40% by weight on a dry basis of the rag pulp, therest of the furnish being refined but substantially unhydrated woodpulp.

The refined cellulose pulps employed in accordance with our inventionare produced by taking the ordinary wood pulps of commerce, such assulphite and kraft, and putting them through the refining action of analkaline liquor under suitable conditions of temperature, time, andconcentration of alkali in the liquor. Thus, the refined wood pulp maybe one which has been prepared by subjecting an unbleached chemical woodpulp, such as sulphite, to the action of hot solutions of caustic sodaor equivalent alkaline refining agents in moderate concentration. Or therefined wood pulp may be one which has been prepared by exposingchemical wood pulp, such as unbleached sulphite or kraft, to the actionof alkaline liquors at about room or even lower temperatures, whosealkalinity is comparatively high and so is capable of extractingnon-alpha cellulose components from the fiber under such temperatureconditions. In some instances, the

refinement of the pulp may take place in alkaline liquors of such highalkalinity and/or at such low temperature as to result in an incipientor complete mercerization, as well as refinement of the fiber. Thislatter effect, that is, mercerization, is had through the use of causticsoda solutions of about 18% or greater strength, at room temperature, orthrough the use of solutions of lower causticity at lower temperatures.A refined pulp whose refinement has been brought about through the useof strong alkaline refining liquors, e. g., liquors of sufficientstrength to be mercerized, is of a puffy and resilient or springycharacter, and consequently must be handled on the felt-forming machinesomewhat differently than-other types of refined pulps. The felts formedfrom such pulps in admixture with rag pulp may require considerablesqueezing or compacting while they are in freshly formed condition onthe wet end of the felt-forming machine, in order to be delivered fromthe dry end of the machine at a compactness such as is desired in theroofing and/or flooring industries, especially the latter industry.Otherwise, they may be too soft and spongy and, after being bituminized,lack the required firmness and defacementresisting qualities desiredmore particularly in a fioor covering material. As hereinbefore noted,however, our felts are in all cases composed largely of the refined butsubstantially unhydrated wood pulp, irrespective of whether such pulphas become incipiently or completely mercerized during the previousrefining operation, or has been preserved in an unmercerized condition.

Inasmuch as refined wood pulp is an essential component in thebituminized sheets of our invention, we wish to define what we mean bythe expression refined wood pulp, so that it may be understood in thepatented claims and their scope be ascertainable. This expression ismeant to exclude the ordinary wood pulps of commerce, such as sulphite,kraft, and soda, whose alpha cellulose content is invariably below 90%.It is designed to include only those preliberated pulps which haveundergone refinement or purification in alkaline liquors to an alphacellulose content upwards of 90% as the lower limit. The refined woodpulp to be used in the felt-making furnishes hereinbefore described maybe one having an alpha cellulose content of about 94%, as thisrepresents a pulp which can be produced economically and yield excellentresults. Refined wood pulps of higher than 94% alpha cellulose contentmay perhaps be employed to better advantage, but their cost ofpreparation is higher, and on this account their use does not appear tobe warranted. It is evidently the removal of that portion of non-alphacellulose components or preliberated wood pulp, such as sulphite andcraft, that conduces to the most marked improvement in the bituminizedsheets whose felt base contains the refined wood pulp as apreponderating ingredient. In other words, the over-all improvementcurve for our bituminized sheets rises sharply as the preliberated woodpulp component undergoes the initial stages of refinement. In any event,however, it is necessary to stay within the range of wood pulps whosealpha cellulose content is above 90%, in order to arrive at bituminizedsheets answering the requirements of our invention.

While it may be possible to treat cellulose pulp from other sources,such as cotton, cotton rags, flax, manila, hemp, ramie, sisal, and thelike, as by suitable treatment with alkaline liquors, and to utilize theprinciples of the present invention in producing the results of thepresent inminimum of effort, equipment, and cost, the production offelts possessed of fine-grained, smooth surface. texture. A bituminizedsheet prepared from such felt can be directly and economically finishedto produce a flooring, for example, having an ornamented face free fromimperfections or blemishes.

We claim:

1. A porous, absorptive, flexible waterlaid felt comprising a blend ofsubstantially unhydrated but alkali-refined cellulose pulp having analpha cellulose content of at least 90% and of beaten and hydrated butunrefined rag halfstufi in amount up to about of the dry weight of theblended fibrous materials, said felt having less tendency to he rupturedat its surface under flexing than a felt made from only saidsubstantially un-= hydrated but alkali-refined cellulose pulp andfurther being less stiff and boardy than a felt made from only saidbeaten and hydrated but unrefined rag halfstuif.

2. A porous, absorptive, flexible waterlaid felt comprising a blend ofsubstantially unhydrated but alkali-refined chemical wood pulp having analpha cellulose content of at least and of beaten'and hydrated butunrefined rag halfstufi in proportion amounting up to about 50% of thedry weight of the blended fibrous materials, said felt having lesstendency to be ruptured at its surface under flexing than a felt madefrom only said substantially unhydrated but alkali-refined chemical woodpulp and further being less stiff and boardy than a felt made from onlysaid beaten and hydrated but unrefined rag halfstuff.

. MILTON O. SCHUR.

WALTER L. HEARN.

